1. Field of Technology and Background
In high speed downlink packet access (HSDPA) facilitating the direction of the radio link from a network to a user equipment (UE), different redundancy versions are created with the two-stage rate matching for the support of an incremental redundancy (IR). The first stage of the two-stage rate matching punctures the transport block such that it fits into the UE soft buffer (configured at the beginning of the connection which also depends on the UE capability). The second stage is used to generate different redundancy versions for the incremental redundancy (IR). It uses either repetition or puncturing. Further details are provided in “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Multiplexing and channel coding (FDD)”, 3GPP TS 25.212, Section 4.5.4. The two-stage rate matching supports both chase combining and incremental redundancy.
For an uplink (UL) enhanced dedicated channel (UL E-DCH) facilitating the direction of the radio link from the UE to the network (e.g., network element), a similar mechanism can be used to generate different redundancy versions, allowing IR to be used in the uplink.
2. Problem Formulation
For HARQ (hybrid automatic repeat request) combining at the network element (e.g., node B, alternatively called base station), the knowledge of the redundancy version (RV) is critical to a decoding process. A wrong value of the RV leads to adverse effects (e.g., corruption of the soft buffer).
3. Prior Art
Because the knowledge of the RV is critical to the decoding process (HARQ combining at the Node B), a first obvious solution is to signal the RV outband (signaling which is sent separately from the data itself) with a strong forward error correction (channel coding) and a strong error detection (through the use of a large CRC). Outband signaling means signaling which is sent separately from the data itself. It is typically protected with its own CRC (cyclic redundancy check) and this channel is coded separately from the data channel. It can be also sent on a separate physical channel (similar to a shared control channel for a high speed downlink shared channel) or it can be alternatively sent on the same physical channel (e.g., dedicated physical data channel, DPDCH) as the data using, e.g., a different transport channel or a physical layer header structure. Unfortunately, using outband signaling leads to a significant overhead, which translates into a significant capacity loss.
An alternative option is proposed by Siemens in the report R1-040207, “Feasibility of IR Schemes for Enhanced Uplink DCH in SHO”, 3GPP TSG RAN WG1 Meeting #36, where it is pointed out that in order to avoid signaling problems, the RV parameters should be calculated implicitly and that can be done, e.g., by determining the parameters from the connection frame number (CFN). Tying the RV to the frame numbering is also known from U.S. Pat. No. 5,946,320, “Method for Transmitting Packet Data with Hybrid FEC/ARG Type II””, by P. Decker.
FIG. 1 shows one example among others of a block diagram for a redundancy version implementation of an uplink enhanced dedicated channel, according to the prior art. In addition to a normal uplink (UL) data signal 22 sent by a user equipment 10 to a HARQ combiner/decoder module 14 of the network element (the node B) 12, the user equipment 10 also provides an outband RV signal 15 containing a redundancy version (RV) parameter (e.g., redundancy version number, RVN) using, for example, a separate uplink (UL) signaling channel, according to the prior art.
The HARQ combiner/decoder module 14 performs decoding and combining the data contained in said uplink data signal 22 and generating corrected data using said outband RV signal 15 and combining with (if it is received) previously received and stored data (e.g., using a soft buffer) redundant to the data contained in the uplink data signal 22. After performing said decoding, it is determined by the HARQ combiner/decoder module 14, whether the corrected data is acceptable according to a predetermined criterion. If the corrected data is acceptable according to said predetermined criterion, the HARQ combiner/decoder module 14 sends a corrected data signal 30 containing said corrected data to a further destination (e.g., another network element such as a radio network controller). However, if corrected data is not acceptable according to said predetermined criterion, the HARQ combiner/decoder module 14 sends a repeat request signal 28 to the user terminal 10 for sending a further redundancy version of said data one more time.